Intersections: who has priority, what the signal obliges, and what a glance costs

Priority at a junction is never a fact about the road. It is always a fact about an instrument — a signal head, a painted triangle, a sign, or, where none of those exists, a default written into a national code. Four junction types are worth holding separately, not because they look different but because a different instrument speaks at each one.

This piece puts those four to the same four questions: who has priority and by what instrument; what the instrument actually obliges; which crash the geometry produces; and what a moment of distraction costs there. It runs in prose rather than as a grid: across four junctions and several markets, most of that grid’s cells cannot honestly be filled.

The signalised crossroads

The instrument is unambiguous — the only one of the four that is. In the United Kingdom, rule 175 requires a driver to stop behind the white stop line unless the light is green, and rule 176 forbids moving over the line while red is showing. Spain’s code says a steady red prohibits passage, and that where the signal sits inside or on the far side of a junction, vehicles must not enter the junction at all.

What the green does not do is more interesting. Spain’s code makes a steady green passage with priority except in the cases of its article 59.1, which forbids entering a junction, even with priority, where you would foreseeably be left stopped across the cross traffic; the Highway Code says the same as a condition, that you go forward on green only if there is room to clear the junction safely. A green light is permission to proceed, not permission to occupy.

The geometry produces the right-angle strike — a side impact into a door, with no crumple structure between bumper and occupant. It is the collision the section’s simulator models as an urban T-bone, and the one where two drivers’ accounts most often differ by exactly one signal aspect. Distraction costs something particular here: the glance that matters is often the one taken at the stop line, which ends with the driver pulling away on a green they did not watch turn. The United Kingdom removes the ambiguity in terms — the hand-held prohibition still applies when you are stopped at traffic lights and when you are queuing in traffic.

The junction controlled by a sign, or by nothing at all

Here the instrument is a sign, a road marking, or a national default — and the defaults differ between markets. The Highway Code’s instruments are the Stop sign with a solid white line, where a driver MUST stop, and the Give Way sign or triangle with broken white lines, where a driver MUST give way to traffic on the main road. Spain phrases the same duty more strongly: at give-way and stop junctions, drivers shall always yield to vehicles on the priority road, whichever side they approach from, coming to a complete halt when necessary.

The divergence is in what happens when nothing is signed. Spain has a written default — absent a sign regulating priority, a driver must yield to vehicles approaching from the right, with listed exceptions for paved over unpaved roads, rail vehicles, roundabouts and motorway traffic. Virginia’s manual states the same rule for a simultaneous arrival, and again when the lights are out: all vehicles must stop, and the driver on the left yields to the driver on the right. The Highway Code does not resolve an unmarked junction by priority at all: its instruction for a failed signal is to treat the situation as an unmarked junction and proceed with great care — a rule about caution, not about who goes.

Spain adds the clause that describes what yielding looks like: the driver who must yield shall not begin, continue or resume the manoeuvre until satisfied it will not force the priority driver to change course or speed abruptly, and must show, by slowing gradually, that they are in fact going to yield. Yielding is a communication, not only an outcome. The geometry is the right-angle strike again, with the struck vehicle usually faster because it was not slowing for anything, and the required action — a long, deliberate look both ways — is exactly what a screen takes away.

The roundabout

The roundabout replaces the crossing conflict with a merge. The Highway Code’s rule 185 says to give priority to traffic approaching from your right unless directed otherwise by signs, road markings or traffic lights. Spain lists roundabouts as an exception to its own yield-to-the-right default: those already in the circulating carriageway have priority over those seeking to enter. Virginia states it for both cases at once — drivers entering any intersection or roundabout must yield to traffic already in it.

What is obliged is therefore a judgement about a moving gap rather than a stop, and Spain’s code requires moderate speed on the approach to any roundabout or junction where priority is not held. The geometry produces entry and exit conflicts rather than right-angle strikes, and the Highway Code names the two that catch people: traffic already on the roundabout may not be signalling correctly or at all, and the vehicle crossing in front of you may intend to leave by the next exit.

The turn across oncoming traffic

The fourth is the unprotected turn across the oncoming stream: a right turn in the left-hand-traffic world, a left turn in Spain and the United States. The geometry is the same, mirrored.

The instrument here is unusual, because there often is none — the turning driver has a green light and still does not have priority. Virginia signs this explicitly: the Left Turn Yield on Green sign tells a driver that traffic turning left at a green light does not have the right of way and must yield to traffic from the other direction. The Highway Code’s rule 180 gives the same duty as an instruction, to wait until there is a safe gap between you and any oncoming vehicle. Spain’s article 74.1 is the strictest of the three: a driver must make sure the speed and distance of vehicles approaching from the opposite direction allow the manoeuvre without danger, abstain if they do not, and abstain altogether from a left turn where visibility is insufficient.

The crash is a misjudged gap that ends as a front-to-side impact, and the Highway Code records a visibility failure inside it: at crossroads where an oncoming vehicle is also turning, passing nearside-to-nearside in front of each other blocks the view of oncoming vehicles, and cyclists and motorcyclists in particular may be hidden by it. Its safer method is offside-to-offside, keeping the other vehicle on your right and turning behind it. Virginia adds one piece of technique: keep the front wheels straight until you are actually going to turn, because a car struck from behind with its wheels already turned is pushed into oncoming traffic.

Distraction costs most here, for a structural reason. This is the only one of the four junctions where the driver is not deciding whether it is their turn but estimating a closing speed, and an estimate made before a two-second glance is not the same estimate afterwards.

The indicator, and what it is not

The Highway Code ends its signalling duties with the sentence «Remember that signalling does not give you priority», tells a driver waiting at a junction not to assume a vehicle signalling left will actually turn, and gives the mechanical reason next — an indicator may not have been cancelled. Spain requires that the warning for a lateral movement end as soon as the vehicle has taken its new line, because that movement is all it announces.

What the glance is actually worth

The best evidence we could read from its publisher is the AAA Foundation’s case-crossover analysis of the SHRP 2 naturalistic driving data, by the Virginia Tech Transportation Institute. It set what a driver was doing in the six seconds before a crash against the same driver’s ordinary driving in matched six-second segments — 566 crashes against 1,749 baseline segments, from 3,593 drivers monitored between October 2010 and December 2013.

Visual-manual phone tasks overall carried an odds ratio of 1.83, confidence interval 1.03 to 3.25, relative to driving with no observable secondary task. Texting alone was 2.22, interval 1.07 to 4.63. Rear-end crashes came out at 7.77, on an interval running from 1.65 all the way to 36.56 — the width is the honest part. Hand-held conversation gave 1.16, interval 0.50 to 2.70, which the report itself calls very imprecise and not statistically significant.

Two things deserve stating. The published stratification is by traffic density, crash severity and crash type, not by junction type, so nothing in it answers the question this article is about. And the widely-quoted twenty-three-fold figure comes from a different study of commercial vehicle operations, which the Virginia Tech Transportation Institute attributes to that study by name on its own pages; it is not the car-driver figure. What both bodies of work say plainly is the part that transfers to a junction: driving is a visual task, and the activities that move the risk are the ones that take the eyes off the road.

Read from official sources, the hand-held prohibition is broader than drivers expect. In the United Kingdom it is illegal to hold and use a phone, sat nav, tablet or any device that can send or receive data while driving, and the law still applies when stopped at traffic lights and when queuing in traffic. Spain’s general circulation regulation, in the version in force since 2006, prohibits using mobile telephony devices or any other means of communication while driving, except where the communication takes place without using the hands and without headsets or earphones. Virginia prohibits holding a phone or other wireless communications device while driving except in a driver emergency or when lawfully parked; its manual states that driver distraction accounts annually for roughly 17 percent of all traffic crashes there.

What we cannot tell you

The instruments above tell you what each junction obliges. They do not tell you what happens afterwards, and two facts decide that. Which of the two drivers is treated as at fault when each says the other’s light was red is the fault system for your jurisdiction, set out in the data below. And whether your own share of the blame reduces what you recover, or extinguishes it entirely, is the negligence rule for your jurisdiction, in the same data below.

The rest is smaller than it looks: four junctions, one instrument each, and one habit that works at all four — find the instrument before you arrive, and keep your eyes on it.